This invention relates to battery charging, and more particularly to the charging of batteries connected together in series.
Many electrical systems utilize batteries connected in series to provide two output voltages. For example, diesel powered trucks, marine equipment, and other utilize a 24 volt or higher supply for starting engines, etc., but require only 12 volts for the remaining electrical components.
In such systems there is presented the problem of providing proper charging of each battery, since they require different amounts of charge. For example, the battery providing the higher voltage output for engine starting generally is used much less than the other and therefore it requires only a few minutes of charge to replace the loss. The battery providing the lower voltage output also is used for engine starting, but has the added demand of the remaining electrical system, and therefore it requires more charge.
Thus, for example, if a regulated 24 volt charge from an alternator is applied at the positive terminal of the higher voltage output battery, the latter becomes fully charged before the lower voltage output battery. However, the voltage regulator sees only the voltage drop across the series-connected batteries, and therefore allows the alternator to continue charging until said voltage is satisfied. As a result, the higher voltage battery is overcharged and the lower voltage output battery is undercharged, causing premature damage to both batteries.
Efforts have been made heretofore to achieve proper charging of each battery in dual battery systems. For example, switching systems have been provided for connecting the batteries in series for starting engines, etc., and for connecting batteries in parallel for charging. However, the additional electrical resistance contributed by the switch results in the higher voltage output battery being maintained in an under-charged condition. The use of two alternators in an attempt to balance the loads, also has been found unacceptable, Special alternators of complex and costly circuitry and physical design have been found to be economically impracticable.
Equally unsatisfactory have been the attempts to circumvent the battery charging problem by using high powered 12 volt starter systems, or by utilizing straight 24 voltage systems for charging and for all other components of the electrical system.